1. Field of the Invention
The present invention relates to a laser annealing method and a laser annealing apparatus, and more particularly to a laser annealing method and a laser annealing apparatus for radiating a laser beam to an amorphous film on a substrate while scanning the laser beam for the amorphous film, thereby crystallizing the amorphous film.
2. Description of the Related Art
In a flat type display device such as a liquid crystal display device or an organic Electro Luminescence (EL) display device, a Thin Film Transistor (TFT) is used as a switching element used to carry out active matrix display by using a plurality of pixels.
A poly-Si TFT in which poly-Si, μc-Si or the like is used in an active region, and an amorphous Si TFT in which an amorphous Si is used in an active region are known as the TFT. Of these poly-Si TFT and the amorphous Si TFT, the poly-Si TFT has the feature that a mobility of a carrier is about ten to 100 times as large as that in the amorphous Si TFT, and thus poly-Si has the very superior characteristics as a constituent material for the switching element.
Here, Japanese Patent Laid-Open No. 2004-87667 discloses a technique for crystallizing amorphous Si. With this technique, a continuous wave (CW) laser beam or a quasi-CW laser beam having a pulse frequency which is as very high as several tens or more of megaheltz is relatively moved (scanned) for a Si film deposited on a substrate in one direction.
With this technique, the crystal is grown along one direction by the scanning the laser beam for the Si film. Crystal grains are formed approximately in parallel with a growth direction. Therefore, with regard to an electrical conductivity in the crystal growth direction, a mobility can be increased because a density of the crystal grains which carriers cross is reduced.